Electronic switching circuit



Aug. 24, 1965 c. R. MADLAND 3,202,904

ELECTRONIC SWITCHING CIRCUIT Filed July 17, 1961 w E A a E E E5 2 '5 5 0 I60 I20 80 4o 0 COLLECTOR TO EMITTER VOLTAGE (VOLTS) Fig.4

INVENTOR.

37 GLEN R. MADLAND ATTY'S.

United States Patent 3,202,904 ELECTRONIC SWITCHING CIRCUIT Glen R. Madland, Phoenix, Ariz., assignor to Motorola, Inc., Chicago, Ill., a corporation of Illinois Filed July 17, 1961, Ser. No. 124,585 9 Claims. (Cl. 323-68) This invention relates generally to transistor circuits for switching and amplifying applications, and in particular relates to a transistor circuit for use in the electrical ignition system of an engine and in other systems where a circuit capable of withstanding relatively high voltages is required.

It has been proposed that ignition systems be provided with an electronic circuit for switching and amplifying the current which is supplied to the ignition coil of the system through the breaker points. One purpose of such a circuit is to reduce the amount of current which passes through the breaker points, and thus reduce wear of the points which is caused by arcing between the points. Transistor circuits have certain well known advantages .over electron tube circuits for such applications. For example, transistors are more rugged than electron tubes and they are operative as soon as they are energized whereas many tubes do not become operative until they warm up. Also, transistors can be expected to have a longerloperating life than comparable tubes. However, known transistorized amplifying and switching circuits had some drawbacks which have held back their widespread commercial use in ignition systems.

One specific problem is that a relatively high voltage, 120 volts or more, may be developed across the primary winding of the coil in an ignition system for an internal combustion engine, and the transistors must be able to withstand this voltage if it appears across the output terminals of the amplifying and switching circuit. Transistors having a breakdown voltage greater than 100 volts are relatively expensive. The required over-all breakdown voltage can be obtained with two or more transistors whose output portions are connected in series, but most multiple transistor circuits of this type have required transformers in the input portion of the circuit which increases the over-all cost of the circuit substantially. The wide speed range of the internal combustion engine requires a wide range of spark frequencies making the transformer design diflicult. Another problem is that in certain multiple transistor circuits which do not employ transformer coupling to the input terminals, there has been a tendency for the transistors to interact resulting in'conduction in one or more of the transistors at times when they should be non-conducting.

Accordingly, it is an object of the invention to provide an improved amplifying and switching circuit for use in automotive ignition systems and other systems which require a circuit that will withstand high voltages.

Another object of the invention is to provide a multiple transistor circuit for switching and amplifying functions having an input circuit portion which prevents conduction of the transistors at times when they should be nonconducting. A further object of the invention is to provide a multiple transistor circuit which has three terminals that are electrically equivalent to the emitter, base and collector terminals of a single transistor, such that the circuit can be handled like a single transistor for purposes of providing coupling into and out of the circuit.

A feature of the invention is a switching and amplifying multiple transistor circuit for an ignition system which includes a combination of diode and resistive elements forming an input portion for the circuit which will supply both direct current and alternating current to the transistors and which prevents the direct current bias voltage from causing any of the transistors to conduct when it is desired that the circuit be non-conducting.

A further feature of the invention is the provision of a transistor ignition system which includes one or more transistors having rectifiers connected in parallel relation with the output paths thereof, with the rectifiers having a breakdown voltage lower than that of the transisors so that the rectifiers conduct when the voltage across the output circuit exceeds the breakdown voltage thereof to protect the transistors from damage by excessive voltage.

Another feature of the invention is the provision of a multiple transistor circuit in which the output portions of the transistors are connected in series and the input portions are connected together by a combination of resistors and diodes so as to form a three terminal amplifying or switching circuit which exhibits electrical behavior-similar to the behavior of a single high voltage transistor, but which is less costly than a single transistor with the same voltage rating.

FIG. 1 is a circuit diagram of an ignition system which includes a multiple transistor circuit in accordance with one embodiment of the invention;

FIG. 2 shows a modified form of the ignition system of FIG. 1 which represents another embodiment of the invention;

FIG. 3 shows still another embodiment of the multiple transistor circuit and in particular shows the three terminals of the circuit which are equivalent to the emitter, base and collector terminals of a single transistor;

FIG. 4 is a graph which shows the electrical characteristics of the circuit of FIG. 3; and

FIG. 5 shows a system in which the circuit of FIG. 3 is represented by an enclosure shown in dotted lines and whose purpose is to supply continuously variable power to a load.

The multiple transistor circuit of the invention includes at least two transistors whose emitter to collector circuit portions orvregions are connected in series relation such that the overall voltage breakdown value of the circuit is the sum of the individual voltage breakdown values of the individual transistors. The base portions of the transistors are connected together to form an input circuit, and the input circuit includes a combination of resistors and diodes arranged so as to supply energizing voltage to the base electrodes of thetransistors and also to prevent undesirable conduction of the transistors as a result of reverse leakage effects or because of the forward biasing of certain emitter-to-base circuits by the bias voltage. The voltage-current characteristics of the over-all circuit are quite similar to those of a single transistor, and the circuit is suitable for both alternating current and direct current amplifying and switching functions. The circuit is particularly useful in automotive ignition systems, and since it does not require the use of transformers or other special coupling circuits in the system, theover-all cost of the system is kept low. Rectifiers may be connected in parallel with the emitter-to-collector output circuits of the transistors which have breakdown voltage values lower than that of the transistors and'which conduct to protect the transistorsvfrom excessive voltage.

FIG. 1 shows the circuit of the invention in an ignition system for an internal combustion engine. In this embodiment the input terminals are 10 and 12, and terminal 19 is a common or ground connection. The breaker points of the ignition system are shown at 13 and these points serve to alternately make and break the connection to ground, thereby turning the transistors 14 and 15 on and oif. When the points are closed, forward bias is applied to the bases of the transistors turning both transistors on. This results in a very low resistance conducting state during this'time. jKWithout rectifier 29 inthe path between terminals 11 and 12, thereby resulting in a current pulse through the primary Winding 16 f the ignition coil 17 V This current is delivered from the battery 18 through an ignition switch 19, and through the a resistor Ztl, Resistor 2v) limits the maximum current that'can'flow when 'the'transistors are turned on. The making and breaking of the'point 13, therefore; producesja changingcurrent through the primary winding 16 of the ignition coil 17, and because the secondary winding 21'v of this ignition coil has very many 'more turns than the primary winding 16,"there is a large step 'tipof voltagethrou gh'the coil, resulting in a very high voltage appearing across the coil secondary winding" 21. This voltage is delivered to the spark plugs of the'engine.

The purpose of the resistors 22 and 23 is to provide a shunt path for the reversetleakage current of the transistorsflfiand 15, thereby preventing the transistors from turning on as aresult of this reverse leakage flow. g If resistors 22 and 23 were not used, the leakage current of the transistors would be amplified through the collector to emitter circuits, and the output circuit would remain on during periods when it was desired to have the output shut "off. Resistors 26 and 27 balance the current outputs of the transistorsythat'is, they make a 'correctionfor differences in'gains between the transistors. Rectifier 28 is aZener diodeand protects transistor from excessive voltages which may cause it to break down andpossibly damage the transistor.

reference numbers. An advantage of locating the igni-- tion coil 17 in the emitter circuit is that base'currents will flow through the primary winding 16 of the coil and therefore add to the energy available to the. secondary winding 21 of the ignition coil. A disadvantage of this configuration as compared to the embodiment of FIG.

l'is that the voltage across the points 13 at break will I be somewhat'higher than the voltage of the battery 18.

The over-all purpose ofjthe circuit of FIG. 2 is the same as that'ofFIG; l and is to-tu'rn the transistors 14 and '15 on and off Ithereby generatingachanging cur- 'rent in the primary 16 of the ignition coil 17. This resuits in aivery high voltage generated in the secondary 21 of the ignition coil 17 an'dthis voltage .is thus available to fire the spark plugsof thefengine. Both of the circuits inFIGS. 1 and 2 utilize the advantage of high frequency 'coil operation with a low inductance coil and high current levels to supply thernecessa ry energy for the secondary of the ignition soil. This provides more available voltage at high engine speeds to main:*

tain engine emciency and also providesgreater ability to fire fouled plugs. g p

' FIG. 3 shows the fundamental circuit of a three" teri minal high voltage system 35. The circuit, which is quite Rectifier "28 v will break down at a voltage below'the breakdown volt: 1

age of'the transistor. 15. Rectifier 29, whichis also a Zener' diode, serves asimilar purpose in protecting the transistor 14. Theflatterfrecti'fier also prevents-the source voltage g18 from forward'biasing the emitter-tobase circuit of transistor 14 since such biasing would turn the device' on during theperiod when the points arelopen. It is desired ,to have the device in a nonagedrops'would exist in resistors 22; 23-,-26-and-27 as a result of the positive voltage existing betweenpoints 12' and 24. t The polarity of the voltage drop existing across resistor 22"would bias the emitter-to-base circuit ofjtransistor 14- positively "thus causing the device to conduct. By using rectifier29 practically all'of the voltage is dropped across the rectifier, biasing in negatively;

and therefore transistor 14 is not caused to conduct; 5 The high voltage thatis generated in-the secondary j 21' of the ingition coil 17 occurs as a-result of the col lapse of the current supplied to the primary 16. The current collapses as a result of the cessationofconduction connected'in series and appears between"te rmin'als"37 and'38. This system is turnedon and olf 'by' application and removal of bias voltage to the input ter-rninals circuit, appreciable volt 'lent to the'emitter element.

36 and 37. The systemexhibits the electrical character.- istics of a single transistor where terminal 36 is equivalent to the transistor base element, terminal 38 is equivaent to the collectorelement, and'terminal 37 is equiva 1 FIG. 4 shows the electrical behavior ofthe three ter minal system of FIG. 3. The collector current as meastired at terminal 38Iis plottedjas the ordinate and the collector-to-emitter voltage, which is the voltage "from terminal "38 to terminal 37, 'isplottedas the abscissa. The various curves branching off to the left represent diftferent values of base current, the larger values of currentbeing at the top. 1 a

The circuit of the threeterminal system of'FIG. 3

' will now be describedin detail. Rectifiers s2, '53 and es (of transistorsl t' and 15. The opening of the points 13 removes the forward bias from'the bases of the tram-- sistors, causing the transistorsto become non conducting; This makes the circuit path from 12 to10 a very high resistance and interrupts't-he current flow to the ignition coil primary 165;;The high voltage developed in thesecondary 21 is proportional tothe product of the secondary inductance and the rate of change of current assume. 1 I

I This- 'config'urationpwith the ignition icoi'l located in the collector circuit, hasfthe advantage as compared to of the Zener type'are connected betweenthe collector and emitter terminals of the transistor'devices 39, 0am 7 41. Each of'these rectifiers serves'the function of prevent ng the voltage appearing across the collector-teal emitter terminals of the transistors' fr orn exceeding the breakdown voltage ofany given transistor. The. recti fiers are-so chosen that thesegrectifiers will breakdown at a voltage less than thebreakdown voltage of the'tran-f sistor with which it is inparallel; thereby. putting a .very

the circuit of'EIG. 2 that the voltage across the points at break is approximately equal to the battery voltage and there is no needtor' a saturation resistor in the col lector circuit. However in FIG. 1' the base currents do not fiow through the coil16 and appreciable'power is dissipated in the base resistances.

FIG. 2 shows an example'ofthe use the ignition :coil 17 is located in the emitter circuit of of the circuitry of the invention in a transistorized ignition-systemswhere thetransstors 14 and15; 'Since most of the circuit com- I ponents in FIG. 2 are connected in the same way and low resistancepath across the collector-to-emitte'r circuit of thetransistor. This prevents any objectionablyhigh voltage from existingfbetween thecollector and emitter terminals. i 1 l I "Resistors 42, 43 and 45 are connected between the base, and'emitter circuits of each of-thetransistor devices 39, ;40:an'd 41 The purpose ofthese resistors is to pro-. yide a shuntpath from the baseto emitter of eachtransistor device to cause most of the reverse leakage current to pass through the resistors rather than allowing "the current 'to pass through'the collector-to-emittercircuit of thetransistors, If these resistors were not used, thetleakage current of the transistor devices would ,turn the dew-1 vices on, thereby providing a low resistance circuit be-1 tween outputterminals 37 and 38 during the timewhen it is desired that the transistors be non-conducting; Thus;

these resistors serve the same purpose as resistors 22 and 23 in FIGS. 1 and 2.

The rectifiers 47 and 48 which are connected in series with the input circuits of the transistor devices 40 and 41 prevent the bias voltage which appears between ter- 'minal-s 37 and 38 from causing untimely conduction of these transistors. If these rectifiers were not present, the negative voltage existing at terminal 38 would forward bias the base-to-emitter circuits of transistors 40 and 41 and cause these transistors to turn on during the time when it is desired that they be non-conducting. Rectifiers 47 and 48 are reversed biased by the bias voltage existing between terminals 37 and 38 and thus exhibit a very high resistance. This causes most of the bias voltage to be dropped across the rectifiers thus preventing an appreciable forward bias from developing across resistor 42 or 45. The purpose of resistors 49, 50 and 51 which are connected in serieswith the inputs to each of the transistor devices, and which are connected together at terminal 36 is to allow balancing of the gains of each of the transistor devices, thereby providing substantially equal outputs from each of the transistors.

The transistor devices 39, 40 and 41 have their collector-to-emitter terminals connected in series; that is, the emitter of transistor 39 is connected to the collector of transistor 40, the emitter of transistor 40 is connected to the collector of transistor 41, and the emitter of transistor 41 is connected to the ground or common terminal 37. Also, the collector of transistor 39 is connected to the output terminal 38. The resistance between terminals 37 and 38 is dependent upon whether or not the string of transistors 39, 40 and 41 is conducting or non-conducting. This in turn is determined by the voltage bias impressed on the input terminals 36 and 37.

This system can be utilized as either a switching device or an amplifier. In switching applications the circuit between the terminals 37 and 38 is either caused to be a very low resistance or a very high resistance, depending upon the bias applied to the input terminals 36 and 37. In amplifying functions, the current introduced into the input terminals 36 is amplified considerably by the system and appears in its amplified form in the circuit between terminals 37 and 38.

FIG. 5 shows an example of the use of the three terminal system 35 to provide adjustable power to a resistive load 61 which, for example, might be a lighting load. It may be desired to vary the intensity of the lights by providing smoothly controlled variations of power to the load 61. In this example the output terminals of the three terminal system are terminals 38 and 37 and the input terminals to the system are terminals 36 and 62. The source voltage 57 is a standard 115 volt 60 c.p.s. voltage. The rectifier 58 provides half wave rectification of the source voltage 57 thereby providing pulses of D.C. voltage across bleeder resistor 59. The voltage across bleeder resistor 59 is fed to the series combination of the load 61 and the system output terminals 38 and 37.

The state of conduction or non-conduction of the system 35 is determined by the point at which the bleeder resistor 59 is tapped by the adjustable arm 63. Zener diode 60 is biased in the conducting direction by the voltage taken off the bleeder resistor 59. The point at which the tap 63 is set on the bleeder resistor 59 determines the portion of the time that the voltage across the bleeder resistor is connected to the load. Because the point at which the bleeder resistor is tapped can be varied, the system 35 can be made to conduct only during the portion of the cycle during which it is desired to deliver the voltage which appears across bleeder resistor 59 to the load. The setting on the tap 63 of the bleeder resistor 59 sets the bias between the emitter and base of the system 35 and therefore determines the point in the cycle when the system will conduct. During conduction a very low resistance path between output terminals 38 and 37 is provided, which connects the pulsating D.C.

voltage through to the load 61. In this configuration it is necessary for the output circuit of the system 35 to be able to withstand the peak voltage appearing across the bleeder resistor 59 which will reach approximately volts during periods of non-conduction. The use of the system to provide this type of control is not limited to a lighting load application but could readily be used for numerous related functions which require variable power.

It is apparent from the foregoing description that the invention provides a multiple transistor circuit having electrical behavior much like that of a single transistor, and which can be readily turned on or ofif by bias changes to its input terminals. The system will perform as a switching device or as an amplifier, and is particularly advantageous in an ignition system. It will perform equally well for both A.C. and D.C. conditions and can handle high currents at especially high voltages.

I claim:

1. A multiple transistor circuit capable of withstanding voltages at the output thereof greater than the voltage breakdown values of the individual transistors, said multiple transistor circuit including in combination, a plurality of transistors each having emitter, base and collector portions, means connecting the emitter to collector paths of said transistors in series to form an output circuit, transformer means having a primary winding series connected in said output circuit, an input circuit having branch circuit portions connected respectively to the base portions of said transistors and having a common connection which is adapted to be coupled to a source of energizing voltage, means coupled to said output circuit and said input circuit for supplying bias voltage to said transistors including resistor elements connected respectively between the emitter and base portions of each of said transistors for shunting leakage current produced in said transistors by the bias voltage, diode means in said input circuit poled to block current in said branch circuit portions due to the bias voltage and to permit flow of current in said branch circuit portions responsive to an input signal for rendering said transistors conductive, and Zener diode means connected to said output circuit and forming a bypass path for preventing breakdown of said transistors due to voltages induced in said transformer means by the conduction of said transistors.

2. A multiple transistor circuit capable of withstanding voltages at the output thereof greater than the voltage breakdown values of the individual transistors, said multiple transistor circuit including in combination, energizing voltage means, first and'second transistors each having emitter, base and collector portions, means connecting the emitter-to-collector paths of said first and second transistors in series with said energizing voltage means to form an output circuit, transformer means having a primary winding series connected in said output circuit, an input circuit having branch circuit port-ions connected respectively to the base portions of said transistors, means providing an intermittent bias voltage coupled to said input circuit, diode means in said input circuit poled to block current in said branch circuit portions due to the energizing voltage and to permit flow of current in said branch circuit portions responsive to the application of bias voltage to said input circuit to thereby render said transistors conductive, and Zener diode means connected to said output circuit and forming a bypass path for preventing breakdown of said transistors due to high voltage in said transformer means resulting from the conduction of said transistors.

3. A multiple transistor switching circuit for use in a spark-ignition system which includes an ignition coil and switching means for providing intermittent pulses, said multiple transistor switching circuit including in combination, first and second transistor means each having emitter, base and collector portions, means connecting the emitter to collector paths of said first and second,

' coil, further means-conneotedto said emitter portion of said first transistor means'to-r applying an energizing voltage thereto,"impedance means connected between said emitter and base portions of each of said transistor means, an input terminal for" connection to the switching means, control circuit means connected to said input terminal and including a portion connected to said base portion of said first transistor means and a port-ion including'resistor means and a first Zener diode connected in series to said base portion of said second transistor means, a v second Zener diode connected between said base and'collector portionsof' said second transistor rneans, said first and second Zenerdiodes being poled toprevent'current flow from said energizing" voltage "through said impedance meansand the ignition coil and to provide 'a bypass-path for preventing breakdown or said-first and second transistor means due to voltages applied thereto from the ignition coil.

4. A multiple transistor switching circuit for use in a spark-ignition system which includes an ignition coil and a pair of intermittently opening breaker points '-'for 1 providing pulses; said multiple transistor switching circuit including in combination, first and second transistors each' having emitter, base and collector portions, means connecting the emitter to collector paths of said first and second transistors inseries, means for connecting said collector portion of said second transistor to the ignition coil, further means connected to said emitter portion of said first transistor for applying an energizingvolt-age thereto, first and second resistor means connected respectively between said emitter and base portions of said first and second transistors, a first resistor connected to said base portion of said firsttransisto-r 'for connecting said base portion to the breaker points, a second resistor and a first Zener diode connected in series to said base portion of said second transistor for connecting said base portion to the'breaker points, a second Zener diode connected across said base and collector portions of said second transistor, saidfirst and second'Zener diodes being poled to block current flow through said resistor means during the, period whensaid breaker points are open, and to permit flow of current through said resistor means upon closure of the breaker points to forward bias said first and second transistors and cause the same to conduct and energize the ignition coil.

5. A transistor switching circuit foriuse in a sparkignition system which includes an ignition coil, switching means and energizing current supply mean-s, said transistor switching circuit including in combination, transistor means having emitter, base and collector portions, means forming a first current path including said emitter and collector portions for connecting the energizing current supply means to the ignition coil, impedance means connected between said base and emitter portions of each of said transistor means, means forming a second current path including'said impedance means connected to the energizing current supply means, means coupling the switching means to said second current path for causingv intermittent energization thereof to'thereby produce intermittent forward biasing of said transistor means and intermittent energization 'of said first currentpath, and Zener diode means connectedbetweenssaid first and second current paths and poled to prevent conduction'frorn said second current path to said first current path, said Zener diode means forming a bypass path when in reverse conduction for preventing breakdown of said transistor means due to voltages in the ignition coil resulting from the intermittentenergization of saidfirst current path.

6. A multiple transistor switching circuit for use in a spark-ignition system which includes an ignition coil, switching means, and energizing current supply means, said multiple transistor switching circuit including in combination, first and second transistor means, each having 8 emitter,-base and collector portions, output circuit means forming a first current path including said emitter and collector portions of. said transistor means for connecting the energizing current supply means tolthe ignition coil, 5 first and second resistors connected respectively between said emitter and base portions of said first and second transistor means, means forming a' second current .path adapted for connection to the encrgizing current supply means tor-forward biasing said'first and second transistor means, said secondcurrent path having first and second branch portions therein, said first'bran'chportion includ-' ing said first resistorand a third resistor in series therewith, saidsecon d branch portion including said emitter and collector portions of said first transistor means and said second resistor and further including a first Zener diode and a fourth resistor in series therewith,-a second Zener diode connected across said collector and base portions of said second transistor means, and means coupling the switching means to said second current path causing intermittent energization of said second current path to therebyproduce intermittent forward biasing of said first and secondtransistor means and intermittentenergization of said first current 'p'ath, said-first andsecond Zener diodes being poled to prevent conduction from said sec- 0nd current path to said first current path. p

7.' A'multiple transistor switching circuit for use in a system'which includes energizing'current supply means, control means and' a load'ir'npedance, said multiple transistor switching circuit including in combination, first and second transistor means each having emitter, base and collectorregion's, output circuit means forminga first current path including said emitter-to-collector paths of said transistor means in series forconnecting the energizing current supply means to the load impedance, first and second resistors connected respectively between said emitter and'base regionsof said first and second transistor means, input circuit means adapted for connection to the'control means and totheehergizing current supply means and forming a second current path for-forward biasing said first and second transistor means, said second current path having first and second branch portions, said first branch portion being cbnnectedto said'base' region of said, first transistor, means and including "said first resistor and a third resistor'in series therewith, said second branch portion being connected to said base region of said second transistor means and including said emitter and collector regions 'of said first transistor means and said second resistor and furtherincluding a first Zener diode and a fourth resistor in series therewith, and a second Zener diode connected between said collector and base regions of said second transistor means, said'coutrol means causing intermittent energization of said second current path to thereby produce intermittent for- Ward biasing of 'saidfirst and second transistor means and intermittent energization of said'first current path, said first and second Zener diodes being poled to prevent conduction 'from said second current path to said first current path. i 1 r i 8. A multiple transistor, switching, circuit for usein a system which includes energizingcurrent supply means, control means and a load impedance, said multiple transistor-switching circuit including incombination, first and second transistor means each having emitter, base and collector regions-output circuit means forming a current path including the emitter-to-collector paths of said tran' sistor means in series for connecting the energizing current supply means to the load impedance, first and sec ond impedance means connected respectively between said emitter and base regions of said first and second transis tor means, input means for connection to-the control means, a. control circuit connected to, said input means and including a first circuit portion connected to said base region of said first transistor means and a second cur-' rent portion includingresistor means and a first Zener diode connected in series to said base region or said second transistor means, and a second Zener diode connected between said base and collector regions of said second transistor means, said first Zener diode being poled to prevent current flow from said energizing current supply means through said impedance means and said control circuit to render said first transistor means conducting, said first and second Zener diodes conducting in response to a predetermined voltage developed across the load impedance to prevent breakdown of said first and second transistor means.

9. A multiple transistor circuit capable of withstanding voltages at the output thereof greater than the voltage breakdown values of the individual transistors, said multiple transistor circuit including in combination, a plurality of transistors each having emitter, base and collector portions, means connecting the emitter-to-collector paths of said transistors in series to form an output circuit, transformer means having a primary winding series connected in said output circuit, an input circuit having branch circuit portions connected respectively to the base portions of said transistors and having a common connection which is adapted to receive an input signal, means coupled to said output circuit and said input circuit for supplying bias voltages to said transistors, diode means in said input circuit poled to block current in said branch circuit portions due to the bias voltage and to permit flow of current in said branch circuit portions in response to an input signal for rendering said transistors conductive, and Zener diode means connected to said output circuit and forming a bypass path for preventing breakdown of said transistors due to voltages induced in said transformer means by the conduction of said transistors.

References Cited by the Examiner UNITED STATES PATENTS 2,832,900 4/58 Ford 323-22 2,891,171 6/59 Shockley 307-88.5 2,899,571 8/59 Meyers 30788.5 2,941,119 6/60 Ford 315-214 2,955,248 10/60 Short 32362 X 2,957,993 10/ Sichling 30788.5 2,963,624 12/60 Meyer et al. 315209 2,966,615 12/60 Meyer et al 315-214 2,981,865 4/61 Fernback 315206 3,016,477 1/62 Naborowski 3l5-206 3,068,392 12/62 Santelmann 32118 LLOYD MCCOLLUM, Primary Examiner. 

6. A MULTIPLE TRANSISTOR SWITCHING CIRCUIT FOR USE IN A SPARK-IGNITION SYSTEM WHICH INCLUDES AN IGNITION COIL, SWITCHING MEAN, AND ENERGIZING CURRENT SUPPLY MEANS, SAID MULTIPLE TRANSISTOR SWITCHING CIRCUIT INCLUDING IN COMBINATION, FIRST AND SECOND TRANSISTOR MEANS, EACH HAVING EMITTER, BASE AND COLLECTOR PORTIONS, OUTPUT CIRCUIT MEEANS FORM ING A FIRST CURRENT PATH INCLUDING SAID EMITTER AND COLLECTOR PORTIONS OF SAID TRANSISTOR MEANS FOR CONNECTING THE ENERGIZING CURRENT SUPPLY MEANS TO THE IGNITION COIL, FIRST AND SECOND RESISITORS CONNECTED RESPECTIVELY BETWEEN SAID EMITTER AND BASE PORTIONS OF SAID FIRST AND SECOND TRANISTOR MEANS, MEANS FORMING A SECOND CURRENTT PATH ADAPTED FOR CONNECTIONN TO THE ENERGIZING CURRENT SUPPLY MEANS FOR FFORWARD BIASING SAID FIRST AND SECOND TRANNSISTOR MEANS, SAID SECOND BRANCH PORTION INCLUDING SAID EMITTER BRANCH PORTIONS THEREIN, SAID FIRST BRANCH PORTION INCCLUDING SAID FIRT RESISTOR AND A THIRDD RESISTOR IN SERIES THEREWITH, SAID SECOND BRANCH PORTION INCLUDING SAID EMITTER AND COLLECTOR PORTIONS OF SAID FIRST TRANSISTOR MEANS AND SAID SECOND RESISTOR ANDN FURTHER INCLUDING A FIRST ZENER DIODE AND A FOURTH RESISTOR AND FURTHER INCLUDING A FIRST ZENER ZENER DIODE CONNECTED ACROSS SAID COLLEECTOR AND BASE PORTIONS OF SAID SIECOND TRANSISTOR MEANS, AND MEANS COUPLING THE SWITCHING MEANS TO SAID SECOND CURRENT PATH CAUSING INTERMITTENT ENERGIZATION OF SAID SECOND CURRENT PATH TO THEREBY PRODUCE INTERMITTENT FORWARD BIASING OF SAID FIRST AND SECOND TRANSISTOR MEANS AND INTERMITTENT ENERGIZATION OF SAID FIRST CURRENT PATH, SAID FIRST AND SECOND ZENER DIODES BEING POLED TO PREVENT CONDUCCTION FROM SAID SECOND CCUURRENT PATH TO SAID FIRST CURRENT PATH. 